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Nautical Terms Relating Sailing and Navigation

Reading about small boat navigation and sailing is like reading a foreign language. Here is a brief intro to sailing and navigation terms that will help you understand better when you read an article or book.

This article came together as I looked up stuff that I did not understand. It is not all inclusive but is a growing concern.

If you want me to add a word, or you know another meaning let me know. It's interesting that many nautical terms differ in meaning depending where you live.

Sailing and Navigation Vocabulary

Points of Sail RADAR Radar Reflector Running Sextan Stiff Weatherly minute of latitude latitude Longitude
Chart Plotter
Navigation instrument that shows charts on a screen. It is usually combined with a GPS and often with a fish finder or depth indicator. The fish finder and depth indicator require a which sends a signal to the chartplotter. The chart plotter can show route travelled as well as the usual gps features.
Small cloth or net like structure that is dragged behind a boat to slow drift or keep the boat lined up. Drogues are used by fishermen to slowly drift down wind or by boats that are being towed to reduce drift and bounce. Drogues are also useful in rough conditions to slow down the boat when going downwind and help stop it from plowing into an incoming wave.
a unit of length equal to six feet or 1.8 metre. Usually used while talking about depth of water.
Global Positioning System. A navigation instrument used to determine position and to help navigate. It works by contacting at least 3 satellites and triangulating position. Because it does not require the sun or stars it is effective in all weather. GPS units are often connected to Chart Plotters for visual displays. It indicates position and speed. My page on GPS
Gybe or Jibe
A jibe (US) or gybe (Britain) is a maneuver whereby a sailboat sailing downwind turns its stern through the wind, so the wind direction changes from one side of the boat to the other making the sail swing to the opposite side. Unplanned gybes can be quite messy and dangerous because the boom can swing very quickly across to the opposite side.
Nautical Mile
A distance unit used at sea. It is defined as 1852 Meters or 6.080 feet or 1.1508 statute miles. It is based on the circumference of the earth at the equator. It is equal to one minute of latitude.
Hull Speed
The maximum efficient speed of a displacement-hulled vessel. Hull speed increases with the length of the hull. When you see a motor boat with its nose way up in the air it is trying to go faster than its hull speed and a huge amount of energy is wasted keeping the nose in the air. Formula :Hull speed in Knots = 1.34 * LWL^1/2. A boat usually cannot exceed it's hull speed unless it starts planing.
A sailing maneuver where a boat turns its bow into the wind. The bow goes across the no sail zone and starts sailing in the opposite direction. It is generally considered safer to tack than to jibe but there is a risk of going in irons and loosing forward momentum if the boat does not have enough speed to carry the bow through the wind.
common logA knot is a measure of speed. It is one Nautical Mile per hour. It is equal to 1.15 statute mile per hour and 1.852 km per hour. The term KNOT comes from the way speed of ships used to be measured. A standard triangular shaped piece of wood was lowered in the water, this piece of wood provided resistance and allowed the rope to be gradually unwound. This rope had knots tied at regular intervals. The wood and rope was called a common log, chip log, ship log, or log. As the rope uncoiled behind the boat, the sailors measured the number of knots that were uncoiled during a measured period of time. The kit came with a standard hourglass with 30 seconds of sand.
image: By Rémi Kaupp - Personal photograph taken in the Musée de la Marine, Paris, CC BY-SA 3.0,
Points of Sail
Part of the inner stem of a boat. The inner top part.
When you draw a boat from measurements, that is you loft it, a baseline is a straight line from which you start your measurements.
Batten Seam
In a batten seam the planks (or plywood pieces) are fastened by gluing or screwing to longitudinal battens, which are usually inside the hull. If the batten connects the side plank and the bottom plank, it is called a chine log.
(Its also a stiffening wood or fiberglass piece used inside sails)
Another meaning of batten is a long flexible rod used to connect the points when you are lofting. (Drawing out the boat from measurements.) The flexible batten connects the points and fills in the curve smoothly.
or breadth (B) is the width of the hull.
The FRONT of the boat.
The lowest inner part of a ship's hull. The parts of a vessel between the lowermost floorboards and the bottom, or where the sides curve in to form the bottom. Bilge Water accumulates in the bilge.
Triangular piece in the bow of a boat. Image is from my Skerry Build
The maximum beam at the waterline
Bearding Line
A line on the side of the sternpost, keel, deadwoods, and stem of a boat that shows where these parts intersect the outer face of the frames. In other words it is where the inside of the planking meets the backbone of the boat, keel, stems etc.
Usually refers to the wooden parts of a boat that are varnished. It sometimes also means the metal parts that are polished rather than painted.
A bulkhead is an upright wall within the hull of a boat. Bulkheads provide support and usually separate different sections to reduce the risk of flooding. In small boats bulkheads might enclose flotation chambers, or might provide rigidity or support a seat.
Decks normally have a slight curvature to assist with drainage and impart stiffness. This is the deck Camber or Crown.
Carvel (or Caravel) Planked
carvel planking is a method of constructing wooden boats by attaching planks to a frame. The planks butt up edge to edge to each other and form a smooth hull. Caulking is required between the joints. It is a heavier method of boat building than Clinker (Lapstrake). When a boat is built a strong frame is first made then the planks are attached to the frame.
A shaped plank often made of metal or weighted wood, which can be pivoted into the water to act as a keel to provide resistance to lateral drift and lift, as well as extra stability. When lifted, the centerboard fits into a well in the hull.
The edge where 2 plank meet. The corner formed when 2 planks come together. If a boat is moulded and round shaped it has no chines. If the boat is made from distinct angles as in plywood boats then it has chines.
Chined or hard Chined Hulls
These are hulls made up of flat panels (commonly made of plywood, or more traditionally with planking) which meet at a sharp angle known as the chine. Grand bank dories are hard chined hulls. Multichine hulls allow a round hull shape to be approximated.
Chine Log
These are pieces of wood to which the 2 flat edges are attached in a hard chined hull and which strengthen the joints. see Chine
Clench Built
Made with planks overlapping downwards and fastened with clenched nails (as opposed to carvel-built, with planks flush). Lapstrake (or clinker built) can be secured with clenched nails or with rivets. Nails were driven through the overlapped planks from the outside, the points were then bent back using a chunky rounded iron dolly. The point was driven back into the planks and stayed in securely. Clenching nails were often iron in Viking ships but copper is more common now.
Clevis Pin
A pin secured by a cotterpin, a ring, or threaded which is used to close a shackle or other fastening. Clevis pins are common on sailboat rigging.
Clinker Built
Similar to Lapstrake. When long boards are overlapped then fastened either with clinched nails or with rivets. This kind of boat construction creates long ridges the length of the boat. This adds rigidity and strength to the hull. Viking boats were Clinker built. Carvel planking makes a smooth hull, Clinker has the ridges.
A shaped plank which can be lowered into the water to act as a keel to provide resistance to lateral drift and to provide lift. Daggerboards are usually found in sailing dinghies. The cross section shape of the daggerboard can have a significant effect on performance. Experts speak of the NACA foils.
The amount of V shape in the bottom of a hull. Deadrise is the angle of the bottom measured upward from the horizontal at keel level. The greater the angle of deadrise, the more v shaped the hull is. The smaller the deadrise, the flatter the bottom of the boat. Its not a constant angle in most boats. Often a boat is more v shaped at the bow and flattens out at the back. The deadrise has implication if the hull is to plane or cut through waves.
Displacement Hull
Hulls that do not plane are called displacement hulls. Hulls that, once they reach a certain speed, stay on top of the water are called planing hulls. Displacement hulls don't generally go any faster than the theoretical hull speed, which is linked to the length of the boat. Planing hulls can exceed hull speed.
Double Ended
Is said of a boat that is pointy at both ends such as a canoe or a peapod.
To Fair
To smooth out. When building a boat great care is taken to smooth out the sides so that curves are smooth and there are no irregularities. This is fairing.
In Stitch and glue boatbuilding, a bead of thickened epoxy is squeezed onto joints to strengthen them. This is a fillet. The process is just about the same as caulking a bathtub.
The sides on the hull of a boat sometimes goes outward as it rises. This is flare. When it comes back towards the inside it is tumblehome. Many old fashioned canoes have tumblehome. Sometimes it is straight up (as in an Optimist).
Wooden boat hulls are usually made of planking attached to frames. In carvel type of boatbuilding the frames are quite substantial and heavy and add a great deal of strength to the boat. In Clinker built or Lapstrake the frames are much lighter and sometimes added after the hull is assembled.
The distance between the water line and the top of the gunwale. Boats designed to be used in quiet water often have very little freeboard such as punts. Boats that typically have to face stronger waves are built with more freeboard, such as dories.
The Board or strake that is immediately next the the keel. The first strake from the bottom.
Part of the rudder hardware. Gudgeons have holes in which pintles fit and make a hinge for the rudder to pivot on.
The upper protective band installed on the top of the sides of the boat. The gunwales are on the outside and often have oarlocks attached to them. Sometimes spelled gunnels. The inside gunwale is called the inwale
A pipe or moulding in a boats side where the anchor rode fits through the hull. Hawsepipes are not usually found in dinghies and small boats but occasionally sailing yachts have them.
A structural board installed on top of the keel to help attach the garboard plank.
A hull deformation which is the opposite of sagging. The hogged keel has a hollow in the middle when the boat is on a flat surface. Sometimes it happens as a wave reaches the middle of the boat and causes it to bend upwards. When permanent it is a defect.
Hull Speed
The maximum efficient speed of a displacement-hulled vessel. Hull speed increases with the length of the hull. When you see a motor boat with its nose way up in the air it is trying to go faster than its hull speed and a huge amount of energy is wasted keeping the nose in the air. Formula :Hull speed in Knots = 1.34 * LWL^1/2
The inside part of the Gunwale. The inwale faces the inside of the boat, the outwale faces the outside.
The central beam running the length of the bottom. It can be quite shallow of quite deep. The shape of the keel determines how well a boat can sail into the wind and how well it can turn or track straight. Boats that are intended to be beached often have a very shallow keel. In sailing yatch the keel is often cast iron or lead. In lapstrake the garboard or first board attaches to the keel. The keel is the backbone of wooden boats. It connects to the stem at the front and back of the boat.
The inside part of the keel is the keelson. It helps make the boat more rigid and strengthens the connection of ribs and other parts of the boat to the keel.
A piece of wood connecting and supporting two parts roughly at right angles. Knees are often seen supporting seats in canoes and wooden dinghies.
Similar to Clinker built. A type of boat construction where long boards (strakes) are overlapped and fastened together along the edge by clinched nails, rivets or glue. Viking boats are a well known example.
Lee Board
Shaped blades which are used as temporary keels. Often seen in boats such as Thames river barges. The Lee board is pivoted from the side of a boat rather than the center of the hull as is the daggerboard. Often 2 lee boards are used and lowered as the boat tacks.
Lining off
The process of projecting the final plank layout onto the hull in boat building
Length Overall, is measured from one end (stern or bow) of the hull to the other end along the center line of the hull.
Mast Partner
A support roughly at the height of the gunwales through which the mast is inserted. The partner supports the mast in its proper position. It can be as simple as a thwart with a hole or can be an elaborate support. The foot of the mast is inserted in the step.
Mast Step
Cuplike depression or support where the bottom of the mast is inserted when stepped. Usually the mast step is supported by the keelson or keel and has drainage to prevent water from sitting at the base of the mast.
The measurements used to Loft. The offsets are usually presented in the form of a table of numbers, the table of offsets. The lofter makes a baseline and marks the offset points then joins them with a flexible batten to get a smooth curve. If you look at old books on boatbuilding you will often see a table of numbers mostly too small to see because they have been reduced from the original. These are the offsets.
The outside part of the Gunwales, inside is inwale.
A line attached to the front of a boat to tow or moor. Usually used on small boats such as canoes, tenders and dinghies.
A pin shaped metal part attached to a rudder. The pintle fits into gudgeons to attach the rudder to the transom or stern of a boat.
Sitting in the boat facing the bow, your port side is on the left. Starboard is on the right.
Push Pull Rudder
A form of rudder tiller that allows the rudder to be controlled from one side or another. The Skerry is built with a push-pull rudder as are many faerings and other scandinavian boats. It keeps the tiller out of the way but requires an adjustment in the steering method at first.
Raked Transom
Transoms can have forward or backward angles or be straight up and down
Another word for angle. Nautical types talk about the rake of the mast, or of the daggerboard. Motorboaters also speak of the rake of the propeller blades.
In wooden boats a rubrail is a protective piece of wood that is installed somewhat below the gunwale along the side of the boat. In fiberglass boats a rubrail is usually vinyl or other plastic strip installed at the gunwale position to protect the boat from bumping injuries. A boat's bumper strip.
If you put a boat on dry land rocker is what makes it rock forward and back. Boat with a lot of rocker turn easily. Drift boats are built with huge rocker to make them ultra manoeuvrable in rapids and fast water.
A small metal plate or washer for a rivet to pass through and be clenched over. Used in lapstrake boat building.
The dimensions or measurements.
A joint in a board or a piece of plywood to make it longer. Usually each side of the board is cut in a long wedge and the 2 sides of the wedge glued together. This increases the glueline and makes a solid scarf. A ratio of 7 times the width of the scarfed board is considered adequate, longer is better. A scarf can also be secured by rivets as are scarfs in faerings.
If you look at the shape of a boat from the side, The top of the hull often curves up (or rarely down) at the bow and stern. This is sheer. Usually the bow and stern are higher to maximize the freeboard at the bow and stern where the boat meets waves. The curve at the keel level is called rocker.
When looking at the boat hull from the side, sheer is the line where the hull meets the gunwale.
A downward or sternward projection from the keel in front of the rudder or in rowboats at the stern. A skeg helps a boat to track straight. A wormshoe is sometimes attached to the sked and provides a replaceable strip to protect the skeg.
The process of measuring a plank to figure out its final shape when on the flat so it can be cut. Sometimes done with a spiling batten. Spelt with only one l.
Vertical post near a deck's edge that supports life-lines. A vertical support under a seat. A vertical support that hold oarlocks when the rower is standing up.
When you are in a boat facing the bow, starboard is on the right. When you are sailing and the wind is coming from starboard and your sail is leaning towards port side, you are in a starboard tack and have right of way over a boat on a port tack.
The stem connects to the keel and extends it to the front and back. Sometimes the stem is carved and decorated.
The back of the boat, bow at the front stern at the back.
A board or plywood panel that runs the length of the boat.
Long thin frames which get fastened to frames and which support planking or strips of wood such as in cold moulding process. Stringers run from bow to stern, in other words lengthwise.
Strip Planking
A method of boatbuilding often seen in canoes and kayaks and smaller dinghies. Strips of wood are glued in position, faired and finished. Minimal forms are used and these are removed after planking.
Stitch and Glue
A very popular amateur method of boatbuilding using plywood panels, stitched with metal wire (or plastic tie wrap) and glued with epoxy. Stitch and glue can produce very sophisticated boats or very simple ones.
Thole Pins
Instead of using metal oar locks some traditional wooden boats sometimes use wooden rods to support the oars. Often seen in Faerings
A side to side support. Canoes typically have at least one central thwart which sometimes double as a carrying rack with shoulder indentations carved in. In other boats the thwarts are sometimes used as seats, as in Dragon boats.
Tombstone Transom
These are small tombstone shaped transoms found on such boats as banks dories. Wherries sometimes have heart shaped transom.
A flat board at the stern of a boat. It can be quite narrow as in Dories or quite wide as in flatiron skiffs. Outboard motors are usually attached to the transom. When boats are designed to be used in breaking waves the transom is often very small to avoid swamping. Wider transom increase the buoyancy of the stern. Transoms sometimes have an indentation in the back to accommodate a sculling oar.
It is present when the beam at the uppermost deck is less than the maximum beam of the boat. Canoes often have tumblehome with the sides curling in somewhat at gunwale level when you look at the shape in cross section.
Refers to the shape of the hull. A hull can be flat bottomed, round bottomed and v bottomed for example.
The line made on the hull on the boundary of water an air when the boat is in the water.
Whiskey Plank
The last plank fastened to the hull of wooden boats. This step is considered cause for rejoicing and often involves a wee shot of whiskey or two.

I try to be accurate and check my information, but mistakes happen.

email me if you find mistakes, I'll fix them and we'll all benefit: Christine